There is a need for devices to provide access to internal regions of a living body, such as the circulatory system or body cavities in circumstances requiring, for example, repeated withdrawal of blood, peritoneal dialysis or injections of drugs, which may be continuous or repeated, into a patient.
While access to the circulatory system is ordinarily gained by use of a needle and syringe, repeated injections may cause scarring and eventual collapse of the vein or infection. Therefore, when repeated injections or blood withdrawals are required, a percutaneous access device is implanted through which access may be gained to the circulatory system and thereafter closed off.
A number of designs for blood access devices have been developed, many of which use a valve which opens and closes to control access to the circulatory system. Problems have developed with such devices because blood may seep into the valve mechanism, causing the valve to stick. Such sticking is especially troublesome because a surgically implanted device is not easily accessible for repairs. Furthermore, blood which has seeped into the valve mechanism is a breeding ground for bacteria which may cause infection in the patient, and stagnant blood or denatured protein in the valve mechanism can cause clotting.
A blood access device is described in U.S. Pat. No. 4,164,221 in which a blood passageway connecting a blood vessel with the outside of the body is blocked by a frustoconical plug. When a valve chamber, including a blood outlet, is secured to the outer end of the passageway, and when a reciprocable stem member is connected to the outer end of the plug, a pull on the stem member relocates the plug to where it allows blood to flow through an annular region in the valve chamber along the plug into the blood outlet at the outer end of the valve chamber. The frustoconical plug has a large area of surface contact with the passageway, and when the displaced plug is reinserted into the passageway, blood is trapped between the periphery of the plug and the passageway. Even when the plug of the device described in the U.S. Pat. No. 4,164,221 patent is pulled fully outward, it is centrally located in the blood passageway and chamber and tends to obstruct the free flow of blood from the blood vessel to the blood outlet.
All blood access devices are inconvenient and unsightly, and for cosmetic reasons, a blood access device should be as small as possible. Obtaining a maximum amount of blood through a small device requires that the passageway leading externally be as large as possible for the size device implanted.
A blood access device for permanent implantation in the human body must also be biocompatible with body tissue to prevent rejection reactions and associated infection. Surfaces which interface with blood should be thromboresistant to prevent blood clotting.
For several medical applications it is desirable to have continual access to body cavities, and in particular to the peritoneum. Access to the peritoneum is required for peritoneal kidney dialysis, which involves pumping a large volume, e.g., about a gallon, of dialysis fluid into the peritoneum and withdrawing the fluid after a period of time during which dialysis is effected. It is well known that certain drugs are more effective if administered peritoneally rather than interveneously, and if a drug such as insulin is to be administered on a continuous basis, an accesssing device will obviate repeated painful administration through the abdomen.
Because of the considerable expense involved in both inpatient and outpatient care, attempts are made wherever possible to supply patients requiring repeated treatment with support equipment by which they alone, or with the aid of relatively untrained persons, may treat themselves. For example, persons requiring repeated doses of insulin are taught to treat themselves. There is also a movement toward home dialysis in order to alleviate the enormous expenses incurred at dialysis centers. Devices which permit self-treatment should be easy to operate and as foolproof as possible. Provisions need also be made for the patient to maintain sterility of internal access devices.
Any internal access device should, of course, cause as little pain and inconvenience to the patient as possible. Thus an access device should be designed for insertion in a manner which will prevent dislodgement of the device by normal activity of the patient.